The present invention generally relates to surgical procedures and, more particularly, provides an improved system for modeling tissue structure. The system of the invention can be used in locating specific tissue structures for both diagnostic and therapeutic purposes, e.g., in pinpointing the location of a tumor during brachytherapy, needle biopsy or the like.
An increasing number of minimally invasive surgical procedures are being developed to reduce the need for major surgery. One problem encountered in many minimally invasive procedures is an inability to see the area of interest within a patient""s body. This has been addressed in a number of different ways. For procedures which are performed within a channel or cavity within the patient""s body, a camera or other remote visualization tool can be used. This tends to work best in large cavities (e.g., in thoracic or abdominal procedures) or in larger non-vascular conduits (e.g., in procedures involving the digestive tract or fallopian tubes).
Certain advancements are being made in visualizing tissue in real time in other procedures as well. For example, ultrasound catheters are gaining acceptance for use in angioplasty and other vascular procedures while a great deal of research effort is being devoted to developing real-time magnetic resonance imaging. For most other procedures, the surgeon""s options are limited to fluoroscopy. The shortcomings of currently available visualization technologies are particularly acute in procedures involving tissue structures within larger tissue masses. For example, current techniques make it difficult for a physician to pinpoint a suspected tumor in the breast during the course of a needle biopsy. In many instances, such tumors are difficult to visualize using fluoroscopy and the physician often must rely on an earlier MRI or CT image as a rough guide in conducting the procedure.
Another procedure that is limited by currently available real-time visualization techniques is interstitial brachytherapy. In interstitial brachytherapy, a radioactive source is implanted directly into and/or immediately around a tissue structure to be irradiated. For example, in treating prostate cancer, radioactive xe2x80x9cseeds,xe2x80x9d which may comprise small spheres of a radioactive isotope, are deposited within and around the prostate organ. While such concentration of the radiation tends to minimize collateral tissue damage, it can be quite difficult to precisely position the radioactive seeds within the tumor because there is no accurate means to visualize the area of interest during the procedure. Instead, a surgeon must rely on a previous MRI, CT or ultrasound image.
Certain highly specialized approaches have been developed to provide real-time feedback during the course of select procedures. For example, a number of techniques have been developed to carefully position an epidural needle within the epidural space of a spinal column. Each of these techniques relies on the principle that the pressure in the epidural space is lower than that in the patient""s tissue or within the arachanoid membrane surrounding the spinal cord itself. When this drop in pressure is detected, a signal is given to the physician or, in some cases, further advancement of the needle is prohibited. Examples of such techniques include those set forth in U.S. Pat. No. 5,517,846 (Caggiani), U.S. Pat. No. 4,940,458 (Conh) and U.S. Pat. No. 4,919,653 (Martinez et al.). While these fluid pressure monitoring techniques work well in placing epidural needles in the epidural space, the utility of this technique in other tissue-related applications is rather limited.
A variety of remote fluid pressure assessing devices are also known in the art. Most of these devices utilize sealed catheters or the like which utilize a pressure transducer. The pressure transducer monitors the pressure differential between the fluid within the lumen of the catheter and the fluid external to the catheter. Examples of such structures are shown in U.S. Pat. No. 5,807,265 (Itoigawa et al.), U.S. Pat. No. 4,456,013 (De Rossi et al.) and U.S. Pat. No. 3,550,583 (Chiku et al.), among others. While such remote fluid pressure sensing devices can be useful in monitoring pulse rate, blood pressure or the like, such fluid pressure measuring systems have limited benefits in procedures focusing on tissue structures.
In light of the above, it would be advantageous in many circumstances to have an alternative means for modeling or visualizing a body structure. It would be particularly advantageous to have such a technique which would allow a physician to better visualize a tissue structure within a larger body of tissue on a real-time basis.
The present invention provides a diagnostic imaging method, a method of detecting a margin of a tissue structure of interest, and a bioresponsive needle system. In accordance with one preferred diagnostic imaging method, the operator is provided with at least one needle having a wall and a distal tip, with a strain gage being connected to the needle wall at two spaced-apart locations. The strain gage generates a strain signal in response to strain on the wall of the needle. The distal tip of this needle is inserted into a patient""s tissue and the needle is advanced distally into the tissue along a first needle path. The strain signal generated during this distal advancement of the needle along the first needle path is monitored. The distal tip of the same needle (or, alternatively, a separate needle having the same structure) is inserted into a patient""s tissue and the needle is advanced distally into the tissue along a second needle path. The strain signal generated during the distal advancement of the needle along the second needle path is monitored. The strain signals generated along the first and second needle paths are correlated with at least two locations along a margin of a tissue structure.
In a further refinement of this technique, the first and second needle paths can follow a prescribed relationship with respect to one another such that the relative positions of the two locations along the margin can be determined. By using a plurality of such needles, a three-dimensional image of the tissue structure can be formed.
An alternative method of the invention permits the detection of at least one margin of a tissue structure of interest, e.g., the margins of a prostate tumor. In accordance with this method, the operator is provided with a needle having a wall and a distal tip, with a strain gage being connected to the needle wall at two spaced-apart locations. The strain gage generates a strain signal in response to strain on the wall of the needle. The distal tip of the needle is inserted into tide patient""s tissue and the needle is advanced distally into the tissue. The strain signal generated during the distal advancement of the needle is monitored and the strain signal is analyzed to detect the margin of the tissue structure. This can be accomplished, for example, by positioning the strain gage distally of a proximal end of the needle such that at least a portion of the strain gage is positioned within the patient""s tissue during at least part of the distal advancement of the needle. If so desired, analyzing the strain signal may include identifying at least one amplitude change, e.g., a sharp discontinuity, in a signal response curve and correlating that change with a margin of the tissue structure.
One bioresponsive needle system of the invention includes an elongated needle adapted to be inserted into a patient""s tissue. Optimally, this needle has a lumen and a wall. A strain gage is connected to the needle wall at two spaced-apart locations, with the strain gage generating a strain signal in response to strain on the wall of the needle. A strain monitor is operatively connected to the needle and is adapted to provide a user with feedback regarding the strain on the needle wall. In one particularly useful embodiment, the needle has a proximal hub, a distal tip and a body extending between the proximal hub and the distal tip. A distal length of the body of this needle is adapted to be inserted into a patient""s tissue, with the strain gage being positioned along said distal length of the body of the needle. If so desired, the needle system may further comprise a motor connected to the needle proximally of a distal end thereof. Depending on the intended application, the motor may advance the needle distally at a constant rate or by applying a constant force.